Olive, Mitotic division of the nuclei of the Cyanophyceae. 23 



Splitting of tliis double spireme into segments to form chromo- 

 sonies; tlie process appears to be ratlier merely a concentration, 

 or ronnding up into small particles, of clironiatin substance, tlms 

 resulting in the formation of minute. sj^lierical, or sometiines 

 irregularly sliaped grannies, which remain imbedded in the achro- 

 matic material. The term „segmented spireme" has been applied 

 to such a condition (AVilson 00, p. 67). We are justified in 

 calling the minute chromatin granules themselves, in such a seg- 

 mented spireme, the chromosomes, by the fact that their number 

 is constant in the cells of plants of the same species. 



It can hardly be doubted that a longitudinal Splitting of 

 the chromosomes occurs, although this is a point very diflicult 

 to determine with absolute certaintv. The middle cells of ha'. 8 

 seem to afford proof for such a conclusion. In the lower of the 

 two cells, the chromatin granule at the extreme left appears to 

 be double, while throughout the rest of the nucleus, there is but 

 one row of granules. In the cell above, this doubling has gone 

 on to a farther extent, so that at both sides of the central body, 

 we can see a double row of dark granules. Even more indis- 

 putable evidence is fm-nished by tig. 13, in which only the un- 

 differentiated, deeply stained nuclear tigure is shown. In this 

 tigui'e, in each of the two cells, it will be noticed that the nu- 

 clear body is deeply divided equatoriaUy by walls which have 

 grown in from the outside walls. Fm^ther, it wiU be seen that 

 a new Splitting is beginning at the edges of the daughter central 

 bodies of the two contiguous daughter cells. In the two farthest 

 separated, we see no such Splitting at the ends. Before the wall 

 iirst formed has completely divided the ceU, a new division has 

 thus begun and a new wall is growing in to meet this plane of 

 hssion. Such an unparalleled example of rapid division occurs, 

 so far as I have observed, only in the two larger species of 

 O.^c'dlatorla. 0. j^rinceps and 0. Froelichia. Careful examination, 

 especially in preparations not so deeply overstained, reveals the 

 fact that a chromatin granule lies at each outer extremity of 

 the Splitting j^ortion of the central body, w^hereas only one such 

 dark body is evident in an undivided end. AVe are therefore 

 justihed in the conclusion that each chromatin granule in a mi- 

 totic iigm-e must undergo fission in a plane parallel to the sub- 

 sequent plane of di\äsion of the cell, thus agreeing with the 

 corresponding phenomenon of Splitting and Separation of chro- 

 mosomes in higher plants. 



Kohl's curious scheme for accomplisliing the equal division 

 of his chromosomes (03, Taf. k, fig. 12) does not bear much re- 

 semblance to the corresponding process occui'ring in the higher 

 l)kmts. This scheme falls to provide for a longitudinal s])litting 

 of the spireme thread, which, instead, is twice transversely seg- 

 mented, a phenomenon which, so far as I am aware, has been 

 nowhere eise observed in the organic kingdom. The first break- 

 ing up of his convoluted thread results in a division into six 

 extremely long straight chromosomes, arranged parallel to the 



